There are large reserves of crude oil in the United States which cannot be recovered. Most of these reserves are found in geologic formations which are considered to have been depleted. Of the 442 billion barrels of oil which have been discovered to date in the United States at various underground locations, less than 25% of the oil has actually been drawn out and about 70 to 75% of the oil has remained in place. The technology of oil recovery techniques has developed with reference to several phases, which have been termed: primary, secondary and tertiary recovery.
Primary recovery was the original method of obtaining crude oil. In general, an internal pressure existed within the oil-bearing formation which was termed "bottom hole pressure". When a well was drilled from the surface down to the formation, this internal pressure would push the oil to the surface where it could be recovered. After the original internal pressure was exhausted, techniques called secondary recovery were employed. In general, this involved pumping water into a reservoit, the so-called water flooding technique. In this way, more oil was swept towards the wells where it could be pumped to the surface. This, and a similar technique called gas flooding, have become known as secondary recovery and are known to boost a given reservoir's average yield from about 30%-50%. Getting to the remaining 50%-70% requires a method to release oil that is either too heavy to be driven by water or gas, is too diffused in the formation, or is trapped by rock and sand.
The techniques for extracting the remaining oil in various formations have come to be known as tertiary recovery. However, of the various techniques used heretofore, none has been totally acceptable or even successful. There are four principal tertiary recovery techniques, of which the most advanced is thermal recovery. In this process the viscosity of the oil is reduced sufficiently to allow it to flow to the well by actually heating the rock formation containing the oil. The heating method is principally the injection of steam into the reservoir. An alternate method consists of actually setting a fire within the formation, which heats the rock and also pushes hot gases ahead of it, causing the oil to flow. However, this method is much too expensive and is not very efficient.
Another technique is hydrocarbon miscible flooding. This method employs light hydrocarbon solvents such as kerosene and the various "dry cleaning" agents. The solvents are pumped into the reservoir, where they mix with the oil and "clean" it from the rock. Obviously, the high cost of solvents places serious limitations upon the process which, at best, is a trade-off between scarce and costly commodities.
A third technique, carbon dioxide flooding, utilizes the property of CO.sub.2 which allows it to dissolve into the crude oil when it is forced into the oil reservoir under pressure. The dissolution of the CO.sub.2 in the oil reduces the viscosity of the oil by a factor of 10 or more. But this system is, at this time, more of a laboratory success than a quantity producer under actual conditions, and it habors a serious drawback which centers around a shortage of CO.sub.2 in this country.
The fourth technique is micellar/polymer (chemical) flooding. The micellar fluid (a solution consisting of special soaps, surfactants, alcohol, oil and water) is injected in "slug" form into the rock deposits to wash some of the oil from the rock. Then a gel-like thickening agent is introduced behind the "slug" injection to help keep the oil moving in the proper direction. This system ultimately could be useful in oil recovery, except that the surfactants are expensive, and it takes almost one year for the oil production to begin after the slug has been injected.
A primary feature of the present invention is that it enables a return to the techniques of primary and secondary oil recovery. In this invention, e.g., through the use of an active hydrogen releasing polymeric material, the crude oil in a subterranean reservoir is caused to generate and release to the formation volatile hydrocarbon gases, which results in the generation of "bottom hole pressure" in selected geological formations. This "bottom hole pressure" may then be used to recover a sizable fraction of the remaining oil in that reservoir. I have also found that I can maintain "bottom hole pressure" for fairly long periods of time, thus permitting substantial recovery of crude oil and other petroleum values from the formation.